1. Field Of The Invention
This invention relates to novel polyols and to the use of such polyols in preparing polyurethanes.
2. Description Of The Prior Art
As is known, the molecular architecture of polyurethanes for many applications, such as, for example, reaction injection molding (commonly termed "RIM") is based upon a distribution of hard and soft segments. The RIM technique is described in Rubber Age, Volume 7, page 46, 1975. The hard segments (i.e., the reaction product of the isocyanate and low molecular weight extenders) provide the modulus requirements, while the soft segments (i.e., the polyol) provide the resiliency or flexibility characteristics. The respective materials or monomers employed contain the reactive moieties at the extreme ends of the molecule. Upon reaction, the molecules are linked end-to-end in a chain fashion.
These polyurethanes are thus block polymers, consisting of the alternating hard and soft segments. The soft segments, most typically polyether polyols, have low glass transition temperatures (T.sub.g), while the hard segments are usually short chain diol or diamine polyurethane or polyureas having a relatively high T.sub.g or T.sub.m. The block character of the polymer causes the hard and soft segments to phase separate into domains. The domain morphology accounts for the advantageous performance properties of such polyurethanes. Thus, when there are at least two hard segments per molecule, a tough elastomeric structure is formed in which the hard domains act as, in effect, bound filler particles that in a sense crosslink and reinforce the soft elastomeric segments.
The domains can be formed by a deliberate step growth polymerization process. However, in many urethane materials, such as in the RIM technique previously described, this domain morphology is formed in situ during the polymerization by a physical chemical phase separation process.
The phase separation process is promoted during the polymerization by the growth of the hard segment molecular weight, increase in the macroglycol molecular weight (i.e., the molecular weight of the polyol and the isocyanate) and the basic incompatability of the hard and soft segments (viz.--the difference in the cohesive energy density). When incomplete phase separation results, what may be termed a "mixed phase" results. The net effect of the presence of a mixed phase is to adversely affect the useful service temperature range of the polyurethane. Thus, an excessive amount of mixed phase increases the room temperature modulus; but, at higher temperatures (e.g., 60.degree. to 80.degree. C.), the mixed phase passes through its glass transition and then behaves as a poor elastomer resulting in a dramatic loss of stiffness and strength. Likewise, at low temperature conditions, problems with brittleness can occur. Annealing the polyurethane can increase the amount of the crystalline hard phase; but the annealing process is time consuming and may cause other undesirable side effects such as, for example, warpage, cracking and the like.
The phase separation process is affected by thermodynamic as well as kinetic factors. Less than satisfactory kinetic control can cause excessive incompatibility between the hard and soft segments. The resulting material in such a situation contains fewer covalent bonds between hard and soft segments, producing a material having poor integrity and what may be termed a "cheese-like" appearance. Premature phase separation can also occur due to inadequate initial thermodynamic factors.
Providing adequate control of the various reaction and process parameters becomes substantially more difficult in conventional RIM processes when high modulus polyurethanes are desired or required. At high hard segment contents, i.e., high modulus formulations, it appears that the phase separation occurs later in the polymerization reaction. The low soft segment concentrations and the viscosity of the reaction mixture at phase separation together with the rigidity of the hard segment polymer seem to kinetically restrict phase separation. In effect, it thus appears that the potential burying of the reactive groups in the crystalline hard segment early in the polymerization process is most likely the cause for this inhibition. The resulting polyurethanes may well fail to exhibit the necessary flexural moduli at various use temperatures. The impact strength, while adequate for fascia parts, is commonly insufficient to provide the properties required for true high performance engineering plastics useful for forming structural parts. Commercial usage of RIM techniques have, for this reason, been generally limited to forming nonstructural parts (i.e., nonload-bearing) such as fascia for the automotive market.
A further problem is that some of the potential applications for polyurethane elastomers would require the use of substantial amounts of low molecular weight chain extenders to achieve the necessary physical properties. The use of ethylene glycol as the extender is highly desirable since the resulting modulus enhancement is superior in comparison to that achieved with higher molecular weight extenders. Unfortunately, ethylene glycol is not compatible in satisfactory amounts with conventional polypropylene oxide-based polyols. Although incompatibility can be tolerated to some extent, the processing problems and limitations created are significant. As one example, bulk shipments and/or storage for even short periods of time become economically unfeasible due to the resulting phase separation of the polyol and chain extender. Even in use, processing often requires continual mixing to prevent phase separation. For this reason, users have often resorted to the use of butanediol which obviates the compatibility problem; but this result sacrifices modulus enhancement (in comparison to the use of ethylene glycol).
One approach to solving these several problems is set forth in U.S. Pat. No. 4,226,756 to Critchfield et al. Satisfactory compatibility and modulus enhancement are provided by utilizing polymer/polyols formed using poly(oxypropylene-oxyethylene) polyols of high ethylene oxide content. The distribution of ethylene oxide in the polyol as well as the amount thereof are essential in providing elastomers with the desired properties. Conceptually, a portion of the ethylene oxide is present as a cap; and the remainder is distributed internally in the polyol chain. Such polyols can tolerate incompatible amounts of ethylene glycol and the like without creating processing problems because the resulting mixture exhibits self-emulsifying properties. The ethylene oxide content of the polyols may be up to 50% and perhaps even more. This approach, however, results in an increase in the amount of ethylene glycol that is solubilized in comparison to the amount which is solubilized when conventional polyoxypropylene polyols are used.
In addition to the previously described techniques, for RIM and other applications, the introduction of hard segments into polyurethanes has been carried out by including in the formulation materials commonly termed polymer/polyols. Polymer/polyols have been described in various prior patents, including U.S. Pat. Nos. Re. 28,715 and 29,118 to Stamberger.
A further and significant application for polyurethanes is in making high resiliency foams, often termed "HR" foam. In this application, rapid reactivity is required for adequate processing. As is known, this necessitates that the polyols utilized possess a relatively high percentage of primary hydroxyl groups since the reactivity of an isocyanato radical with a primary hydroxyl is considerably faster than is the case with a secondary hydroxyl group. The utilization of ethylene oxide in polyoxypropylene polyols can be used to increase the percentage of primary hydroxyl groups. However, this improvement in reactivity may well be at the expense of undesirable adverse performance characteristics. More specifically, due to the typical relatively high surface area of HR foams, the inclusion in the polyol of significant amounts of ethylene oxide may well have adverse effects on the desired humid aging properties of the foam.
Great Britain Pat. No. 1,042,833 describes oxyalkylated derivatives of glycerol which have a large percentage of primary hydroxyl groups. These compounds are prepared by reacting an alkylene oxide and ethylidene glycerol in the presence of a basic catalyst and thereafter hydrolyzing to provide the polyol.
European Patent Application EP No. 43,966, filed Jan. 20, 1982, describes the alkoxylation of compounds such as 2,2-dimethyl-1,3-dioxolane-4-methanol with oxirane or the like. The alkoxylate is treated with an alkyl isocyanate or an acid chloride to block the terminal OH group and is then treated with an acid to cleave the dioxolane ring, giving a surfactant containing two hydroxyl groups derived from the cleaved ring.
U.S. Pat. No. 2,629,740 to Carnes describes the preparation of polyether amines, i.e., hydrolyzable N-substituted polyether amines. A plural-carbon aldehyde or ketone such as acetaldehyde and an alkoyl amine such as ethanolamine are reacted to provide a 2-substituted oxazolidine. The oxazolidine is than reacted with a compound such as ethylene oxide, glycidol or the like. It is stated that it appears the epoxy compound adds at the nitrogen atom of the oxazolidine ring, and that a fairly large number of moles of epoxy compound (up to 100) may be so added, creating in effect a polyether side chain terminating in hydroxyl. The compound remaining is hydrolyzed with water, whereby the original aldehyde or the like and the polyether secondary amine are formed. These compounds are disclosed as being valuable as intermediates, particularly in the synthesis of surface active agents and for other purposes.
Despite the prior efforts, there continues to be the need to provide a polyurethane system capable of adequately satisfying the many diverse requirements of RIM techniques and extending potential end uses without suffering any penalties insofar as performance and the like are concerned. Still further, when using polymer/polyols to form at least a portion of the hard phase, it would be desirable to minimize or eliminate the mixed phase which results when using conventional polyols in the polymer/polyol preparation. The need exists to provide polyols having adequate reactivity for HR foam applications, yet which achieve the necessary processing characteristics without adversely affecting the foam characteristics desired.